What’s the maximum amount I can invest at one time?
The maximum you can pay into an ISA for the 2019/20 tax year is £20,000. The annual Lifetime ISA contribution limit is £4,000. Please note that the £20,000 ISA limit is shared between any ISAs you have open in that tax year (including Cash and Stocks & Shares ISAs and Lifetime ISAs).
There is no limit to what you can invest in a GIA, but there is a £20,000 limit to the amount you can invest in any one week.